Many of today's electronic devices interact with some form of media in a repeated automatic fashion. Examples of media include paper, cardboard, fabric, polymers and the like. Such electronic devices typically include feed devices that automatically and repeatedly supply individual sheets or pieces of media to a mechanism that interacts with the individual sheets or pieces of media. For example, many scanning electronic devices include automatic document feeders that feed individual sheets along a path to a scanning mechanism. Printers and copiers frequently include an automatic document feeder that feeds individual sheets of media along a path to an inkjet or an electrophotographic printing mechanism.
In some of such systems, it may be desirable to accurately and precisely detect the positioning of the media as it is being fed along the media path to properly sequence the feeding of individual sheets, to initiate scanning or printing at the proper time and to identify malfunctioning of the electronic device or jamming of the media within the device. At the same time, it may be desirable that any mechanism used for detecting the position of media within the device be compact, simple to manufacture and assemble as part of the device, and inexpensive.